Would a FH really fit into a 55? If it is only a female, then forgert it cause they just look like regular fancy chichilids to me. A FH, Bichirs, red devils or an oscar are the top choices right now aside from alot of other fish in the tank like a few pearl gouramis, sharks, loaches, corys, angelfish, etc. I might even get a bigger tank like a 75 or 100gallon from glasscages.com or by searching on craigslist. If i do get another 100+ tank, i will get another aro or something.